Drought-Beater Soybeans

Think Different: Luck or Genetics
Drought stricken soybeans that pushed yield records had several advantages:
Perfectly timed August rains.
Reproductive resilience. While corn has only one chance to develop an ear and tassel, soybeans can abort many flower flushes and still produce more. Soybeans can compensate if environmental conditions change.
Normal August day and night temperatures.
Deep roots; some reported at 5, 6, 7 and even 9-ft. depths to find moist soil.
Drought suppressed pests and disease.

While the drought ravaged many Midwestern corn fields in 2012, soybeans in many of those same areas broke yield records. Field averages of 70, 80 and 90 bu. with spikes well above that were reported throughout the upper Midwest. Extension crop specialists contacted by Corn & Soybean Digest credit the ever-resilient soybean's response to late-season rains. And to the role the hot dry weather played in reducing insect and disease pressure.

"The 2012 season was the most unusual I have seen in 32 years of Extension work in Illinois and Michigan due to the heat and the drought," says Ned Birkey, Spartan Agricultural Consulting and former Michigan Extension educator, field crops. "This was our seventh year for Michigan soybean yield contests and the first where we documented a 100-bushel yield. We had three yields in the 90 to 99 bu./acre range and six in the 80 to 89 bu./acre range."

While the top three yields were on irrigated acres, non-irrigated Group 2 beans came it at 90.1 bu./acre; Group 3 non-irrigated dropped to 67.6 bu. Birkey points to an 8-in. variation in rains across the 15 counties with entrants. He also points to an absence of insect pests aside from an early spider mite infestation. Disease was also down, though Birkey gives much credit here to expanded fungicide use in recent years.

“To go from ankle-high in July to an average of 60.2 bushels at season end is pretty phenomenal,” says Laura Lindsey, Ohio State University assistant professor, soybean and small grain production. "When I visited our Henry County location in early July, the soybeans were only ankle high. However, they got 6.5 in. of rain in August, well above average, and soybean performance trials there averaged 60.2 bu./acre, with a high of 74.6 bushels and a low of 39."

FEWER PESTS

Lindsey says disease was simply not a topic of discussion this past season, and insects were limited to spider mites at one location and a few bean leaf beetles in the fall. "Other areas weren't as dry as Henry County, but also didn't get the August rains, so they had lower yields," she says. "Our longer season varieties did better due to rain timing."

Iowa growers saw a drop in soybean yields in 2012, but it was much less of a drop than they saw in corn, notes Andy Lenssen, cropping systems agronomist, Iowa State University. Protein levels also were notably diminished. Lenssen points to the drought's effect on nitrogen fixation and availability during reproductive stage as affecting protein and yield.

"A 50-bushel soybean yield requires more nitrogen than the average corn crop," explains Lenssen. "The first response to drought during the reproductive phase is to slow and then stop nitrogen fixation. The drought also reduced microbial breakdown of organic matter by soil bacteria, as they also died back. About half the nitrogen in soybean seeds comes from sybiotic (symbiotic) fixation and the other half comes from residual nitrate and the breakdown of organic matter. "

He credits the ability to produce good yields in the face of the 2012 drought to soybean reproductive resilience. While corn has only one chance to develop an ear and a later, narrow window to pollinate, soybeans can abort many flower clusters and still produce decent yields.

"Soybeans can compensate if environmental conditions change," says Lenssen. "Our daytime and nighttime temperatures got back to normal in August, and we had some rain. We continued under drought conditions, but the soybeans had access to deeper soil moisture."

DEEPER ROOTS

Lenssen advised soybean growers who asked if their crop was dying to check soil moisture. He reports that some pulled backhoes into fields and found that soybean roots reached 5, 6, 7 and even 9-ft. depths to find moist soil.

Like his counterparts to the East, Lenssen reports very little disease this past year, and without excess moisture, iron chlorosis was also not a problem. Sudden death syndrome, brown stem rot and Phytophthora were all largely absent, as were most insects.

"Most diseases need sustained, relatively high humidity, and we didn't have enough humidity or inoculum to have even moderate levels of foliar disease," notes Lenssen. "We had some Japanese beetles early, and two spotted spider mites were more frequently seen than in most years, as they respond to really dry and dusty conditions. Even where growers had possible yield reduction early in the season, when the weather turned cooler and wetter, the plants compensated with new growth, leaves and racemes, and flower clusters."

Even though some areas were dry in 2012, a moisture-rich soil profile from previous years helped North Dakota soybeans do well this year, according to Hans Kandel, North Dakota Extension agronomist. "Even the worst areas in North Dakota got some rainfall, but there were regions that were definitely way below annual precipitation levels," he says. "As the season unfolded, root systems were able to tap into that stored soil moisture. A lot of the production came from soil moisture. We are monitoring the water table, and it dropped below our 6-ft.-deep observation wells. That hasn't happened in the past six years or more."

The drier conditions did produce a drier canopy than normal, notes Kandel. As a result, North Dakota soybean growers saw very limited disease. "We often battle Phytophthora root rot, but it was definitely less this year," he says. "Other diseases were also at a minimum, and we ended up with a fairly healthy crop."

Better than average yields for North Dakota were in the 30s, though North Dakota varietal trials produced yields in the 50, 60 and even 70 bu./acre range in dryland conditions and as high as 85 bu./acre in irrigated plots.

"Growers and myself were surprised with the yields," says Kandel. "Though we didn't have rain in that critical period, we ended up with a very good crop. The warmer than normal year also contributed to yields, as most of our beans were mature before frost, with even the longer maturities filled out completely."